//给定两个整数数组 preorder 和 inorder ，其中 preorder 是二叉树的先序遍历， inorder 是同一棵树的中序遍历，请构造二叉树并
//返回其根节点。 
//
// 
//
// 示例 1: 
// 
// 
//输入: preorder = [3,9,20,15,7], inorder = [9,3,15,20,7]
//输出: [3,9,20,null,null,15,7]
// 
//
// 示例 2: 
//
// 
//输入: preorder = [-1], inorder = [-1]
//输出: [-1]
// 
//
// 
//
// 提示: 
//
// 
// 1 <= preorder.length <= 3000 
// inorder.length == preorder.length 
// -3000 <= preorder[i], inorder[i] <= 3000 
// preorder 和 inorder 均 无重复 元素 
// inorder 均出现在 preorder 
// preorder 保证 为二叉树的前序遍历序列 
// inorder 保证 为二叉树的中序遍历序列 
// 
//
// Related Topics 树 数组 哈希表 分治 二叉树 👍 2007 👎 0


package leetcode.editor.cn;

// [105]从前序与中序遍历序列构造二叉树

import java.util.HashMap;

public class ConstructBinaryTreeFromPreorderAndInorderTraversal_105 {
    private class TreeNode {
        int val;
        TreeNode left;
        TreeNode right;

        TreeNode() {
        }

        TreeNode(int val) {
            this.val = val;
        }

        TreeNode(int val, TreeNode left, TreeNode right) {
            this.val = val;
            this.left = left;
            this.right = right;
        }
    }

    public static void main(String[] args) {
        Solution solution = new ConstructBinaryTreeFromPreorderAndInorderTraversal_105().new Solution();
        solution.buildTree(new int[]{3, 9, 20, 15, 7}, new int[]{9, 3, 15, 20, 7});
    }
    //leetcode submit region begin(Prohibit modification and deletion)

    /**
     * Definition for a binary tree node.
     * public class TreeNode {
     * int val;
     * TreeNode left;
     * TreeNode right;
     * TreeNode() {}
     * TreeNode(int val) { this.val = val; }
     * TreeNode(int val, TreeNode left, TreeNode right) {
     * this.val = val;
     * this.left = left;
     * this.right = right;
     * }
     * }
     */
    class Solution {
        int[] preorder;
        int[] inorder;
        HashMap<Integer, Integer> map;

        public TreeNode buildTree(int[] preorder, int[] inorder) {
            map = new HashMap<>(inorder.length);
            for (int i = 0; i < inorder.length; i++) {
                map.put(inorder[i], i);
            }
            this.preorder = preorder;
            this.inorder = inorder;
            return process(0, inorder.length - 1, 0, inorder.length - 1);
        }

        private TreeNode process(int lp, int rp, int li, int ri) {
            if (lp > rp || li > ri) {
                return null;
            }
            TreeNode node = new TreeNode(preorder[lp]);
            int index = map.get(preorder[lp]);
            node.left = process(lp + 1, lp + index - li, li, index - 1);
            node.right = process(lp + index - li + 1, rp, index + 1, ri);
            return node;
        }
    }
//leetcode submit region end(Prohibit modification and deletion)

}